The work described in this proposal is part of a long-term effort to elucidate basic processes critical for the precise synaptic wiring of the nervous system. Appropriate synaptic connectivity emerges during development and is fundamental to establishing complex cognition and behavior in humans. Clarifying the mechanisms of normal development is necessary in order to subsequently understand aberrancies that occur in human neuro-developmental disorders, such as autism. The involvement of synaptic adhesion molecules in the induction of synapse formation and their potential role in establishing synaptic specificity, makes this class of proteins an important focus for neuro-developmental studies. One key family of postsynaptic adhesion molecules, the neuroligins (NLs), can induce presynaptic formation via association with presynaptic binding partners, called neurexins. The focus of this proposal is on one particular NL isoform, NLS, which has been implicated in autism-spectrum disorders. Expression, localization and function of NLS are currently poorly understood. The goal of this proposal is to elucidate the role of NLS in synaptogenesis at the cellular and biochemical level. Aim 1 investigates the expression, subcellular localization and receptor-ligand interactions of NLS, specifically with respect to its regulation by alternative splicing. In Aim 2, the ability of NLS to recruit specific synaptic proteins and to induce the formation and functional organization of pre- and postsynaptic compartments will be examined. Experiments will use a combination of cellular assays in dissociated hippocampal neurons, molecular biology approaches, and biochemical methods to probe protein-protein interactions between NLS isoforms, neurexins, and neurotransmitter receptors. The results obtained in the proposed experiments will yield a detailed functional characterization of NLS that will provide the basis for understanding cellular defects associated with autism-spectrum disorders.